1. Field of the Invention
The present invention relates to a tire vulcanizing apparatus, and especially relates to a heating device for use in the vulcanizing apparatus in which a metal mold for the tire vulcanization is heated by induction heating with the aid of electromagnetic induction coils.
2. Related Art Statement
Heretofore, as to a method for heating the metal mold used in the tire vulcanizing apparatus, there has been proposed a method for contacting a high-pressure steam or a high-temperature heat medium with the metal mold, or a method for heating the metal mold by a resistant heater. However, there are various drawbacks in the above methods such as a complicated maintenance operation and a low heat efficiency, and thus a further improvement is required.
In order to eliminate the drawbacks mentioned above, there has been proposed, in a Japanese Laid-open Publication No. 114,042/84, a tire vulcanizing apparatus in which a tire is vulcanized by inductively heating a metal mold by means of the electromagnetic coil. However, in this known tire vulcanizing apparatus, since a cylindrical coil is wound around an outer wall of the metal mold corresponding to a tire tread portion, a diameter of the coil must be substantially equal to that of the metal mold for the tire vulcanization. Therefore, the electromagnetic coil is made large in size, and the heat efficiency is made low because the coil has no magnetic core. Further, in the tire vulcanizing apparatus mentioned above, since a magnetic flux is passed through a portion other than the metal mold i.e. a vacant portion of the tire, there occurs a drawback that an inductively induced eddy current is not distributed uniformly over the metal mold and thus a uniform heating can not be achieved.